Light and Atmosphere 1

Transcription

1 Light and Atmosphere 1

2 Vibrational Modes Electronic Energy States: With molecules there`s an addi3onal complexity. e - In addi3on to electronic energy levels, molecules have vibra&onal energy levels. p + p + t 1 p + p + t 2 p + p + e - p + p t + 3 p + p + t 4 p + p + t 5 2

3 Rotational Modes Electronic Energy States: Moreover, each vibra3onal state has separate rota&onal energy sub- levels. e - p + p + Mode 1: p + p + (Out of page) e - Mode 2: p + p + (in plane of page) 3

4 Atmospheric Absorp3on Earth s Spectra Kiang et al., Astrobiology,

5 Atmospheres of other planets Transit Detec3on 5

6 Atmospheres of other planets Transit Detec3on HD Balister et al., Nature,

7 Atmospheres of other planets HD209458b s Spectra Spectra of (star+planet) Spectra of star = Spectra of planet Red curve is the 1600 K blackbody of the planet divided by the 6000 K blackbody of the star Richardson et al., Nature,

8 Atmospheres and Surfaces of other Mars Spectra Atmosphere planets Surface Bishop et al., Nature,

9 Solar Spectrum at Earth Kiang et al., Astrobiology, 2007 In visible, spectrum above and below Earth s atmosphere, same shape. è Fraunhofer lines not due to absorp3on by Earth s atmosphere 9

10 Depositing Energy Energy from the Sun may be transmitted directly to the ground, absorbed in the atmosphere, or reflected from clouds or the Sun back into space. Some re-radiated heat from the ground is absorbed by the atmosphere, further heating it. What s going on? Moon Earth 10

11 Atmospheric Layers: The temperature gradient (whether it increases or decreases with altitude) is set by the type of absorption that occurs. We can affect this! Photo- disassocia,on & Ioniza,on Spontaneous Emission Photochemistry Sca$ering Hea,ng from Ground Thermosphere/Ionosphere Mesosphere Stratosphere Troposphere 11

12 Spaceship One Flight Date Top speed Al3tude Dura3on Pilot 12G March 11, km/h km [4] 18 min 30 s Peter Siebold 13P April 8, 2004 Mach km [4] 16 min 27 s Peter Siebold 14P May 13, 2004 Mach km [4] 20 min 44 s Mike Melvill 15P June 21, 2004 Mach km [4] 24 min 05 s Mike Melvill 16P September 29, 2004 Mach km [4] 24 min 11 s Mike Melvill 17P October 4, 2004 Mach km [4] 23 min 56 s Brian Binnie Source for data and figures: Wikipedia

13 Atmospheric Transmission: Not all of the Sun s Light Reaches the Ground! 13

14 Atmospheric Layers and Solar Input: Summary LETHAL 14

15 Atmospheric Layers and Energy: Look at the solar blackbody spectrum. The regions of the spectrum that directly affect the atmosphere are only a tiny fraction of the total! 15

16 Molecular Absorption: Peak of Sun`s spectrum Peak of Earth`s spectrum H 2 O CO 2 Human Eye Sensi,ve. Our eyes are well matched to our star and atmosphere! The atmosphere lets the Sun`s energy in, but doesn`t let the Earth`s energy back out! 16

17 Light interacts with the gases in the atmosphere in several ways: 1. Scagering: photons interact with the medium and con3nue in a different direc3on 2. Photo- dissocia3on/ photo- ioniza3on: photons ionize atoms and molecules or dissociate molecules 3. Fast par3cle: collisions causes an e - to jump energy levels and fall; a photon is emiged 4. Airglow: recombina3on, chemical reac3ons, & Radiative Transfer: Photo- dissocia,on or Photo- ioniza,on Fast par,cle (aurora) Sca$ering of incoming light Incoming light Spontaneous Internal Source cosmic rays (airglow) 17 Atmosphere

18 An Example: The Role of Ozone Ozone photochemistry heats the stratosphere. Ozone is an example of a molecule composed of oxygen. (O 3 ) Ultraviolet radiation both forms and destroys Ozone. Ozone layer absorbs 93-99% of UV radiation. Without Ozone the UV radiation would reach the ground and kill most living things on the surface of the Earth. 18

19 An Example: The Role of Ozone Peak ozone concentra3on 19

20 Why we should care. Human activity is destroying the Ozone layer!! Chlorofluorocarbons (from spray cans) are transported to the stratosphere. They contain chlorine. Chlorine is very bad, because it destroys Ozone. Cl + O 3 ClO + O 2 ClO + O Cl + O 2 The above is called a catalytic reaction. The O 3 is destroyed, but not Cl! Because the stratosphere is stable, the Cl is trapped. This is a big problem. Ozone destroying chemicals are regulated by the Montreal Protocol. Scientists estimate the ozone will return to pre 1980 conditions by